Recent clinical studies have strongly suggested that there is a correlation of Prevotella intermedia, a gram-negative black-pigmented obligate anaerobic rod, with the development of periodontal disease. This organism is frequently isolated from periodontal lesions associated with various forms of periodontitis and is generally accepted as a putative periodontopathic organism. It is recognized that for this microorganism to survive and emerge as a potential pathogen in a host, one of the prerequisites is its ability to adhere to host tissues or to other bacteria. The frequent isolation of P. intermedia from periodontal lesions suggested that this organism may possess the ability to adhere and to colonize host tissues. However, little is known regarding the adherent properties that may be associated with this subgingival bacterium. In our earlier observations of oral strains of P. intermedia, unique surface appendages (fimbriae) were observed on these organisms. Isolated fimbriae from these bacteria were capable of binding to various mammalian erythrocytes, an expression of adherence activity. The working hypothesis of this proposed study therefore is to determine whether or not the fimbriae of P. intermedia may contribute to the pathogenicity of this organism by mediating adherence of this organism to host cells. The long- term objectives are: (1) to determine the adherence mechanisms of P. intermedia to host cells; (2) to establish the function of the component(s) which mediate adherence of the organism by generating isogenic mutants which lack the adhesive component(s); (3) to test the in vivo subgingival colonization by P. intermedia wild type cells versus the mutants; and (4) to test the native or recombinant adhesin as a vaccine to prevent, eliminate, or reduce infection in the subgingival crevice of squirrel monkeys. The specific aims of the proposed work will be: (1) to purify and characterize the adhesive component(s) which mediate the binding of P. intermedia cells to host cells; (2) to identify the functional domain(s) of the adhesive component(s) and to characterize the molecule(s) using monoclonal antibodies raised against the adhesin(s); (3) to characterize the morphological and biochemical events leading to the binding of the adhesive molecule(s) to host cells; and (4) to clone gene(s) encoding the adhesive molecule(s) and characterize the gene(s) and their product(s). The results of these studies should provide information regarding the molecular mechanisms which would promote subgingival colonization by P. intermedia.